CO2 Injection Effects on Low-Field Nuclear Magnetic Resonance Response

We performed CO2 injection experiments on a saturated Berea sandstone core and a Niobrara mudpack to determine presence and magnitude of changes in low-field Nuclear Magnetic Resonance (NMR) response with CO2. Such NMR response changes can then be investigated to determine total CO2 adsorbed by rocks of differing mineralogies and to detect preferential pathways for CO2 created by dissolution. We recorded changes in NMR relaxation for low pressure CO2 injection in these differing rock types. Transverse relaxation (T2) experiments for acquiring the NMR signals were made with a low-field (2 MHz) MagritekTM NMR. The ProspaTM program was used for data inversion. T2 magnetic relaxation was acquired using Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences. CO2 was injected at a pressure of 50 psi with an ISCOTM syringe pump in an NMR pressure vessel made of torlon plastic. Results were obtained for a Berea sample, a Niobrara mudpack, and for both samples measured simultaneously. CO2 injection in the Berea core leads to a decrease in the relaxation time of the spectra data and an increase in signal amplitude at faster relaxation times. In the Niobrara sample, little shift in the relaxation time and smaller signal amplitude variation is seen.